DEXTER  Tony T. Walker, a Fort Drum soldier en route to Atlanta, was among the passengers who boarded the first flight to Philadelphia Thursday at Watertown International Airport.

The 23-passenger flight on the 50-seat US Airways Express Bombardier CRJ200 aircraft, which left about 2 p.m., signaled the end of flights to OHare International Airport in Chicago. The switch followed the merger of American Airlines and US Airways, after which the new combined airline streamlined operations at rural airports where it receives federal subsidies to offer flights.

American Eagle, a subsidiary of American Airlines, began offering flights to Chicago in fall 2011 at the Watertown airport, off Route 12F in the town of Hounsfield.

Mr. Walker, stationed at Fort Drum for six months, booked a flight for the first time at the county-owned airport. Mr. Walker learned that flying to Philadelphia offered him a better route home to Atlanta than he could get from Chicago. He said Fort Drum soldiers who live on the East Coast or in the South told him they will benefit from the flight switch. Flights to Philadelphia are now offered at the Watertown airport twice daily, seven days a week.

Ive talked to three guys about flying to Chicago, and they live in Philadelphia, Georgia and Florida, said Mr. Walker, who is spending Mothers Day weekend with his family in Atlanta. They had to fly to Chicago and then come back, so this is a lot more convenient for them.

Defending the switch from Chicago to Philadelphia, American Airlines has touted the better reliability of flight service thanks to the closer hub. Passengers should enjoy fewer flight cancellations, the airline said. The flight distance from Watertown to Philadelphia is 250 miles. To Chicago, its 535 miles.

Even so, the convenience of the switch depends on ones destination. Chicago was a more convenient destination for Fort Drum soldiers who live in the Midwest and West. Business leaders in the community advised Jefferson County and airline officials against making Philadelphia the new hub. Michael J. Hawthorne, president of New York Air Brake, said the companys use of the Watertown airport will decline by one-third to one-half because it does much of its business in Chicago.

Jefferson County legislators responded to the criticism by saying they had no choice but to accept the flight switch. The choice was: give up the Chicago flights and take the Philadelphia route, or risk losing air service altogether. The airline receives an annual subsidy under the federal Essential Air Service to offer flights in Watertown. But it can pull out of its two-year contract with Jefferson County.

On Thursday, the first inbound CJR200 plane from Philadelphia arrived about 1:20 p.m. Daniel T. Connell of Watertown was among 12 passengers who debarked from a 50-seat plane operated by US Airways Express  an upgrade from American Eagles 44-seat Embraer 140 jet. US Airways will switch to a 37-seat Dash 8 turboprop at the airport in the fall because of stricter weight restrictions. The airport may use large jets year-round if the county completes its proposed 1,000-foot runway expansion.

Mr. Connell took a flight back to Watertown Thursday from Chico, Calif., his original home. He flew to California by making a stop in Chicago but came home via the Philadelphia hub.

Im used to going to Chicago at OHare, he said. That has been the norm, and I had never been to Philadelphia before. But its actually a nice airport, and I like it better than Chicago. Its more upscale, and there are more places to eat.

Visiting friends in Pennsylvania and New York City also will be more convenient by flying to Philadelphia, Mr. Connell said.

If Im going to places in Pennsylvania, I could be there with just a couple of small hops in about two hours, when I would drive there in six to eight hours, he said. I think this kind of opens up more options for someone living in Watertown. Some people who used Chicago will lose options, but I think having a closer hub is a good change.

County Legislator Philip N. Reed, R-Fishers Landing, said some residents criticized the flight switch while others have praised the move. Mr. Reed is a member of the Jefferson County Board of Legislators General Services Committee, which oversees airport operations.

Some people say theyre going to miss Chicago, while others say they want to go through Philadelphia, he said. Youre not going to make 100 percent of the people happy, but that is our goal with the service we offer here. Philadelphia has better reliability for getting in and out of the location, but Chicago was below average for that. Its important that passengers get in and out on time.

A temporary reduction in passenger traffic is expected at the airport as people become familiar with services offered by the Philadelphia hub, Jefferson County Administrator Robert F. Hagemann III said.

While overall passenger traffic climbed in 2013, the number of passengers affiliated with Fort Drum dropped, Mr. Hagemann said. This suggests that the airport, which draws passengers from Canada, shouldnt be significantly hampered by troop reductions at the military base. A $25,000 market study now underway will help officials pinpoint where passengers are coming from and develop marketing plans.

The number of Fort Drum customers went down and the total number of our passengers has gone up, but we dont know why, Mr. Hagemann said. But thats something that this study is going to help us find out. We think that this is partly due to our market in southeast Ontario, where we have a strong customer base.